From U.S. Pat. No. 3,940,985, an ultrasonic flow measuring device is known, in which volumetric flow rate of a medium flowing in a pipeline is measured radius-dependently. In this known solution, a plurality of pairs of ultrasonic sensors are arranged on the periphery of a measuring tube. These ultrasonic sensors deliver measurement data concerning flow velocity of the medium in different segments of the measuring tube. For ascertaining the volume flow of the medium through the pipeline, the measurement data from the individual measuring paths are integrated with suitable weighting.
From WO 97/19326, an ultrasonic flow measuring method is known, in which velocity of a medium flowing in a pipeline is ascertained along different measuring paths of an ultrasonic flow measuring device. In order to improve measurement accuracy, viscosity changes measurement are considered in the flow measurement. Changes in viscosity of a medium are caused by temperature changes, for example. In order to take such into consideration, it is proposed in WO 97/19326 to determine, by measuring the Reynolds number, a correction factor, with which the flow profile dependence of the flow measuring device can be compensated. For ascertaining the Reynolds number in WO 97/19326, the ratio of the flow velocities measured in the different measuring paths is used. In this known solution, a correction of the flow profile dependent measurement error is, thus, only possible, when, first, the Reynolds number is explicitly ascertained or measured. Such a method is relatively complex, both in the calibration phase and in the subsequent, measurement operation.